The present invention relates to a timing device for time switch.
Such type of a conventional timing device comprises a switch 1, an operating lever 2 for the switch 1, and time scale 3 disposed on the front surface of the timing device as shown in FIGS. 1-5. The timing device further comprises a scale plate 6 possessing plug-in portions 5 each consisting of a slot 51, a groove 52 and a frame 53 and for fitting a presetting element 4 thereinto, and such plug-in portions being arranged on the circumferential part of the scale plate so as to correspond to the respective time scales, presetting elements 4 each having -shape being capable of inserting the same to fit into the aforesaid plug-in portion 5, a clock mechanism 7 and the like parts.
In this arrangement, if a presetting element 4 has previously been fitted into the plug-in portion 5 at the position corresponding to a desired time scale on the scale plate 6, such scale plate 6 is rotated by means of the clock mechanism and when the prescribed time passed away, the lever 2 is shifted from a state illustrated by means of broken line to a state shown by solid line, in other words, the lever 2 is shifted in counterclockwise direction by means of the presetting element 4 inserted to turn the switch 1 ON. Further, when time elapsed and the presetting element 4 passed through the lever 2, the same is returned to the state illustrated by broken line to turn the switch OFF.
Referring to FIGS. 1 and 2 showing an example of a time switch in which the minimum presetting interval is fixed at 15 minutes, so that (24.times.60)/15=96 plug-in portions are formed on the scale plate 6. Namely, this means that when one presetting element 4 is inserted in a plug-in portion, the switch 1 may be kept ON for only a period of time of 15 minutes from the time corresponding to the inserted position. Furthermore, when n presetting elements 4 are inserted in n plug-in portions in succession, the switch 1 can be kept ON state for a period of time of n.times.15 minutes from the time corresponding to the initial inserted position of a presetting element 4.
Referring now to FIGS. 3 and 4 which show an example of a time switch in which the minimum presetting interval is fixed at 30 minutes, so that (24.times.60)/30=48 plug-in portions 5 are formed on the scale plate 6. Thus, when one presetting element 4 is inserted in a plug-in portion, the switch 1 can be kept ON for only a period of time of 30 minutes from the time corresponding to the inserted position of the presetting element. In the case when n presetting elements 4 are fitted in n plug-in portions in succession, the switch 1 can be kept ON for a period of time of n.times.30 minutes from the time corresponding to the initial fitted position of a presetting element 4.
In the above stated conventional time switches, both the scale plate 6 and presetting elements 4 shown in FIGS. 1 and 2 are made of a metal material, respectively, whilst both the scale plate 6 and presetting elements 4 shown in FIGS. 3 and 4 are made of a plastic material, respectively.
In the former time switch (FIGS. 1 and 2), even if a thickness of the presetting element 4 is thinned, a sufficient elastic force of the scale plate 6 as well as a strength required for the operation of the lever 2 can be obtained. Accordingly, the former time switch 1 has an advantage in that the minimum presetting interval can be fixed at a small value. On the other hand, however, since the plug-in portions 5 must be worked by means of press-cutting in this type of the time switch, a thickness T of the scale plate comes to be substantially equal to a width l of each slot 51 and groove 52. For this reason, the former time switch has a disadvantage in that an inserted presetting element 4 easily topples in the rotational direction of the scale plate 6 at the resiliently engaged portion as its fulcrum, so that it is difficult to keep the position of the element so inserted in the prescribed position. In addition, with decrease of a thickness of a presetting element 4, a thickness of a cutting blade in a press tool for cutting plug-in portions 5 of the scale plate 6 becomes also thin. Besides a number of such thin cutting blades are required for the fabrication of the former time switch 1, and as a result the greatest possible care is necessary for the press operation. Moreover, there is also such a disadvantage that considerable costs and man-power are required for maintaining manufacture properties of such press tool in respect of the former time switch 1.
As compared with the former time switch, the latter time switch (FIGS. 3 and 4) has advantages in that it is excellent in the mass productivity and can be inexpensively manufactured, besides it becomes easy to thicken a thickness of the scale plate 6, so that toppling of a presetting element 4 can be prevented to easily keep the position of the presetting element inserted in the prescribed position. However, in order to obtain a sufficient elastic force for the scale plate 6 and a strength required for operating the lever 2, a thickness of the presetting element 4 must be thickened, so that the minimum presetting interval increases. Thus, there is such a disadvantage that if the minimum presetting interval is identical to that of the former time switch, an external dimension of the scale plate 6 must be increased. In addition, the latter time switch has a disadvantage in that a dimension of the opening of a -shaped presetting element 4 expands and deforms by means of stress relaxation phenomenon of plastic material due to change in ambient temperature and the like phenomena thereby to lose the elastic force upon the scale plate 6, and as a consequence the presetting element 4 inserted falls off from the plug-in portion 5.